Synthetic polymeric and inorganic membranes are used widely in several areas for aqueous separations. Some specific examples include use in dairy, food, pharmaceuticals, industrial processes, and municipal water treatment. Two persistent issues in these membrane systems that increase their energy use are 1) concentration polarization where solute builds up on the membrane surface and reduces driving force for transport of solvent, and 2) colloidal particle and microorganism deposition on the membrane that eventually leads to fouling and performance deterioration in these systems.
It is commonly accepted that in pressure driven separation processes such as reverse osmosis (RO), particulate foulants primarily deposit on the membrane surface due to convective filtration whereby particles that cannot penetrate the membrane are deposit on the membrane surface. The resulting cake layer hinders back diffusion of salts due to tortuosity leading to an enhanced buildup of a high salt concentration at the membrane surface. This salt buildup is higher than what would be expected in the absence of a cake layer due to hindered diffusion of salts away from the membrane, which is typically referred to as Cake Enhanced Concentration Polarization (CECP). The increase in salt concentration at the membrane surface enhances osmotic pressure leading to high flux decline. The performance deterioration results in lower productivity, solute leakage and loss of membrane integrity.
As such, there is a need for new materials and processes of preventing or reversing the causes of membrane performance deterioration.